Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Treasury Stock [Member]	AOCI Attributable to Parent [Member]	Total
Balance (in shares) at Dec. 31, 2014	32,836,930
Balance at Dec. 31, 2014	$ 3,284	$ 119,265	$ 188,481	$ (14,823)	$ (44,981)	$ 251,226
Net income			57,217			57,217
Other comprehensive income (loss)					(10,468)	(10,468)
Exercise of stock options (in shares)	691,985
Exercise of stock options	$ 69	5,747				5,816
Vested restricted stock		(76)		76
Stock option expense		2,975				2,975
Restricted stock expense		353				353
Performance stock expense		2,271				2,271
Excess tax benefits		1,445				1,445
Balance (in shares) at Dec. 31, 2015	33,528,915
Balance at Dec. 31, 2015	$ 3,353	131,980	245,698	(14,747)	(55,449)	310,835
Net income			81,678			81,678
Other comprehensive income (loss)					(10,071)	(10,071)
Exercise of stock options (in shares)	398,680
Exercise of stock options	$ 40	4,901				4,941
Vested restricted stock		(92)		92
Stock option expense		3,816				3,816
Restricted stock expense		489				489
Performance stock expense		3,461				3,461
Excess tax benefits		10,278				$ 10,278
Vested performance shares		(1,152)		1,152
Balance (in shares) at Dec. 31, 2016	33,927,595					33,927,595
Balance at Dec. 31, 2016	$ 3,393	153,681	327,376	(13,503)	(65,520)	$ 405,427
Net income			102,450			102,450
Other comprehensive income (loss)					23,292	23,292
Exercise of stock options (in shares)	343,380
Exercise of stock options	$ 34	4,747				4,781
Vested restricted stock		(83)		83
Stock option expense		4,368				4,368
Restricted stock expense		571				571
Performance stock expense		3,975				3,975
Vested performance shares		(1,280)		1,280
Balance (in shares) at Dec. 31, 2017	34,270,975					34,270,975
Balance at Dec. 31, 2017	$ 3,427	$ 165,979	$ 429,826	$ (12,140)	$ (42,228)	$ 544,864